How Is Carcinoma of Unknown Primary Classified?

If your doctor still cannot find the primary site of the cancer after doing a number of different tests, you may be officially diagnosed with carcinoma of unknown primary origin (CUP). A pathologist will review the biopsy samples and typically classify the cancer as one of these five most common types:

Squamous cell carcinoma

Adenocarcinoma

Poorly differentiated carcinoma

Neuroendocrine carcinoma

Poorly differentiated malignant neoplasm

The pathologist's classification of the cells from the biopsy will help your doctor to determine a treatment plan, even if the original site of the cancer remains unknown.

Doctors will repeat a careful physical exam and maybe some of the prior tests. They will have a second pathologist look at the biopsy samples. Sometimes, as time passes, a small hidden primary tumor may become large enough to be found. This may help the doctors reclassify the CUP.